Variable density window



April 8, 1941. E. H. LAND VARIABLE DENSITY WINDOW Filed Nov. 1 0'.. 1958'llllllllllllllll Illll//Illlllllllllll Patented Aprk 8, 1941 VARIABLEDENSITY WINDOW Edwin H. Land, Boston, Mass., assignor to PolaroidCorporation, Dover, Del., a corporation o! Dela- Application November10, 1938, Serial No. 239,796

Claims.

This invention relates to variable density windows.

An object of the invention is to provide a variable density windowcomprising a plurality of overlying light-polarizing elements and meansassociated therewith for controlling at will the amount of lighttransmitted thereby.

A further object of the invention is to provide a variable densitywindow of the character described wherein one of the light-polarizingelements is fixedly positioned and the other element movable withrespect thereto.

A still further object of the invention is to provide such a windowwherein the movable element is movable linearly with respect to thefixed element and wherein the motion of the movable element imparts apredetermined stress or strain to material showing photoelastio effectsand positioned between the polarizing elements.

A still further object is to provide such a window wherein thelight-polarizing elements are xedly positioned with respect to eachother and the density of the window as a whole is altered by alteringthe tension on a sheet of material showing photoelastic eiiects andpositioned between the polarizing elements.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises an article of manufacture possessingthe features, properties, and the relation of elements which will beexemplified in the article hereinafter described and the scope of theapplication of which will be indicated in the claims.

For a fuller understanding of the nature and objects' of the inventionreference should be had to the following detailed description taken inconnection with the accompanying drawing, in which- Fig. 1 is a view insection of one form of the invention;

Fig. 2 is a view in front elevation of the device shown in Fig. 1;

Fig. 3y is a view in section of a still further modication of theinvention; and

Fig. 4 is a view, partially in elevation and partially in section, ofthe device shown in Fig. 3 taken along the line l-l.

Heretofore, when it has been necessary or desirable to reduce theintensity of light transmitted by a window in a dwelling, vehicle, orthe like, the desired result has been accomplished by drawing across thewindow a supplemental translucent or opaque substance, such as a shadeor curtain or blind. Speaking generally this has resulted in animpairment or complete destruction of the clarity of the image visiblethrough the window, or at least through those portions of the windowover which the shade or blind has been drawn. As a result it has beenfound that frequently a considerable portion of the window area performsno useful function, except on rare occa sions. This is particularly truein railroad vehicles, where the upper portion of the window almostinvariably remains covered by an opaque curtain or screen, only thelower portion being usefully employed. So also in dwellings it isfrequently customary to leave a shade or curtain drawn over aconsiderable portion of the window area or to hang drapes or curtains orsimilar light-obstruction elements so as to block appreciable portionsof the window areas.

The control of light intensity at the windows has thus been accomplishedfrequently by a restriction of the window aperture usefully employed. Inother cases it has been accomplished by drawing across the window acurtain, screen or the like which completely destroys the transparencyof the window unit and makes it impossible for a person positionedWithin the vehicle, dwelling or the like to see through the window.

It is an object of the present invention to provide a variable densitywindow of a character such that the intensity of the light transmittedVthereby may be controlled accurately from a predetermined maximum tocomplete cut-oi, if desired, without obstructing the clarity of theimage transmitted by the window, at least until the point ofsubstantially complete cut-off is reached. This may be accomplished byproviding a pair of overlying light-polarizing elementseach preferablysubstantially the size of the full window aperture and by the provisionof means for moving a transparent element, for example one of thepolarizing elements with respect to the other of the elements, so thatthe intensity of the light transmitted by the combination of elementsmay be controlled.

In one form of the invention the movable element may be slidably mountedwith respect to the xedly positioned polarizing element, and the twoelements may have their polarizing axes positioned at right angles toeach other or parallel to each other, and preferably in a direction ordirections substantially at 45 to the direction of motion of the movableelement with respect to the xed element. For example, if the movableelement is to be moved vertically, the polarizing axis of the iixedelement. may be inclined at an angle of 45 to the vertical in the planeof the element, and the polarizing axis of the movable element may besimilarly inclined and may be either parallel to or at right angles tothe axis of the fixed element.

With such a structure an intermediate transparent layer, showingphotoelastic effects when extended, may be employed between the twopolarizing elements, and this layer may preferably be of such acharacter that when it is subjected to an extension of predeterminedamount it becomes a half-wave plate or shows half-wave retardation, andhence causes a rotationin the plane of polarization of light transmittedby the polarizing element nearest the light source such that thedirection of vibration of that light is rotated through an angle of 90.Under these circumstances, if the two polarizing elements werepositioned to block light initially-the stress or strain in theintermediate layer will result in a combination of elements such thatthe window transmits incident light, whereas if the elements werepositioned initially to transmit a maximum of light, the strain in theintermediate layer would result in a condition such that the incidentlight is blocked by the two polarizing elements.

In this form of the invention the intermediate layer may be extendedindependently of any motion of the polarizing elements, or it may be soaixed to the polarizing elements as to be responsive to relative linearmotion of one of said elements with respect to the other. It willI beapparent that a preferred structure contemplates the provision ofsurfaces of relatively large area.. as the intensity of lighttransmitted through the entire window should preferably varysimultaneously over all portions of the window area. This implies theuse of lightpolarizing material of large surface area. Such a materialis available under the trade name polaroid, one form of which, forexample, comprises asuspension of polarizing particles in alight-transmitting medium, the particles being oriented with theirpolarizing axes parallel and so distributed throughout the medium as toimpart substantially uniform polarization to a transmitted beam. Apreferred form of this material for use in the present invention is ahigh concentration of polarizing crystals, such as crystals ofiodosulfate of quinine or iodosulfate of cinchonidine in a very thinfilm or layer of a light-transmitting plastic, preferably the materialsold under the trade name Vinylite XYSG. Films of this material of lessthickness than .0003 inch have been found to be excellent polarizers.Such films are now available in areas at least as great as any desiredfor use in the present invention.

It may be desirable to employ films or sheets of the above typelaminated to or between sheets of glass or other rigidlight-transmitting supporting media,l and the use of such polarizingmeans is preferred. It is to be understood, however, that any otherlight-polarizing elements of `large area, or adapted to be assembled toform large areas, may be employed in the present invention. It will beapparent that for satisfactory results the sheets or lms of -polarizingmaterial employed should be relatively thin and highly efficient, and ifit is necessary to piece out the area by lamination or by overlappingsmaller areas oi"4 polarizers the materials employed should be of acharacter such that large areas may be# produced without the appearance'of unsightly overlaps.

Where a photoelastic bonding material is to be.

' 50, 5 2, each providing a polarizing surface, preferably in the formof a thin adherent illm 54, 56. These films are preferably on the innerfaces of their supporting plates. Each of the plates and its associatedlmmay be mounted, as shown in Fig. 1, xedly in the frame of the vehicleor dwelling in which the window is employed.

Between the elements 50 and 52 there is provided a layer of a material58 showing photoelastic effects when subjected to extension. Thismaterial may comprise, for example, a polymerized incomplete polyvinylacetal resin, such as the material sold as Vinal, an acrylic acid esteror the like. It is preferably present in such thickness as to showsubstantially a half-wave retardation when subjected to a predeterminedstress or strain.

Such a stress may be imparted to the sheet 58 by means of the apparatusshown in Fig. 1. The upper edge of the sheet may be rmly held as at 60between the frames of the window elements. The lower edge of the sheetmay be aixed by any suitable means 62 to a roller element 84 in the baseof the inner window element. The roller 64 may be provided with a gear66 adapted to mesh with a worm 68 which in turn may be driven byrotation of the handle 10.

The polarizing films 54, 56 are preferably so positioned that theirpolarizing axes, indicated generally by the arrows 12, 14, are at rightangles to each other and at angles of 45 to the direction of extensionof the element 58. Under these circumstances the strain set up in thematerial 58, which is a directional strain corresponding to thedirection of extension of the element, will be at an angle of 45 to eachof the polarizing axes, and if the material 58 acts as a half-waveretardation plate, it will cause a rotation in the direction ofvibration of polarized light transmitted -by either of the elements 54,56. Thus, if the axes 12, 14 are atright angles, the window as a wholewill be most nearly opaque when no strain is on the material 58, and thewindow as a whole will transmit the most light when the strain on thematerial 58 is such that it acts as a half-wave plate.

'I'he material 58 is preferably selected of such thickness that arelatively slight extension, for example less than one inch, will impartto it the desiredv stress. It is preferably also resilient orrubber-elastic, i. e., it tends to return to its initial unstrainedstate when the tension is released. If desired, stops may be provided inconnection with the roller 64 to prevent too great a stress beingapplied to the element 58. Under certainl circumstances, and where it isdesired to impartcolor to the light traversing the win dow. elements,the sheet 58 may be stretched a considerably greater amount, for exampleso that I it no longer acts as a. half-wave device.

A still further modication of the invention is SRCH RO' shown in Figs. 3and 4. In this form two window elements 500 and 520 are provided, eachcoated on its inner face with a polarizing layer 540, 5". Intermediatethe window elements there is provided a resilient, extensible element580, adapted when stretched a predetermined amount to function as ahalf-wave plate. This sheet 580 is aflxed along one of its edges to thewindow element 500, as at 582, and along its opposite edge to the windowelement 52B, as at 584.

One of the window elements, for example the element 500, is mounted forvertical motion, linear and parallel to the flxedly mounted element 52.This motion may be accomplished in any suitable manner, for example bysupporting the element 500 on one or more cam members 600. which in turnrest upon a sliding bar or rack 602 provided, as shown in Fig. 4, withsimilar and cooperating cam surfaces.

Motion of the bar 602 to the right in Fig. 4,

i. e., in the direction of the arrow 6M, results in a camming actionwhich raises the window element 500, moving it with respect to theelement 520 so as to impart the desired stretch to the sheet 580. Motionof the bar 602 in the other die rection permits the window element 500to fall to its initial position, thus relieving the stress on theelement 580. If desired spring means GIB may be provided to insure aprompt return of the element 500 to its lower position.

Knob means BIZ may be provided affixed to the bar 602 to facilitatemotion thereof.

It is to be understood that the polarizing axes of the elements 560 and5&0 are positioned pre!- erably in the same manner as those of the eledments 56 and 54 in the device shown in Fig. 4 and that the stressapplied to the sheet 580 is similar in the results achieved to thatapplied to the sheet 58.

In any of the devices shown in Figs. l, 2, and 3 and 4, the spacebetween the window elements and surrounding the extensible sheet may befilled, if desired, with a liquid lubricant. Preferably the liquidshould have a low vapor pressure and an index of refractionapproximately that of the extensible sheet. A very thin llrn of liquidis adequate. It may even be present initially in the extensible sheetand be worked or pressed therefrom in the assembly and operation of thedevice.

Any of the devices shown and described may be actuated by motor means(not shown) remotely controlled in any suitable way. For example, allthe windows of a car or dwelling may be adapted to be simultaneouslyoperated and the intensity of light transmitted accurately controlledfrom a central control station. All such modications are to be deemedwithin the scope of the invention.

Although the window elements in Figs. l, 2, 3 and 4 are shown aspermanently mounted in the dwelling, vehicle or the like, it is to beunderstood that they and their associated and related elements, forexample the entire assemblage shown in Fig. 1, may be mounted for motionwth respect to the dwelling or vehicle wall. so that the window may beopened and air admitted to the dwelling or vehicle.

Since certain changes may be made in the above article and differentembodiments of the invention could be made without departing from thescope thereof, it is intended that all matter contained in the abovedescription or shown in the accompanying drawing shall be interpreted asillustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all 4the generic and specic features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secureby Letters Patent is:

1. A variable density window for illumination purposes comprising, incombination, frame means providing a window aperture of substantialarea, a plurality of sheet-like, light-polarizing elements at least ofsubstantially the same area as said aperture, means for mounting saidelements in substantially parallel relation within said frame, a sheetof light-transmitting, resilient material at least of substantially thesame area as said aperture adapted when subjected to a predeterminedstress to function as a halfwave retardation device, means for mountingsaid sheet between and overlying said polarizing elements, andreleasable means for subjecting said material to said predeterminedstress to vary the amount of light transmitted by* said window.

` 2. A variable density window for illumination purposes comprising, incombination, frame means providing a window aperture of substantialarea, a plurality of sheet-like, light-polarizing elements at least oi'substantially the same area as said aperture, means for mounting saidelements in substantially parallel relation within said frame, a sheetof light-transmitting, resilient material at least of substantially thesame area as said aperture adapted when subjected to a predeterminedextension to function as a halfwave retardation device, means formounting said sheet between and overlying said polarizing elements, andreleasable means for subjecting said material to said predeterminedextension to vary the amount of light transmitted by said window, saidpolarizing elements being positioned with their transmission axes atangles of substantially 45 to the direction in which said extendingforce is applied.

3. A variable density window for illumination purposes comprising, incombination, frame means providing a window aperture of substantialarea, a plurality of sheet-like light-polarizingelements at least ofsubstantially the same area as said aperture, means for mounting saidelements in substantially parallel relation within said frame, a sheetof light-transmitting, resilient material at least of substantially thesame area as said aperture positioned between and overlying saidpolarizing elements and adapted when subjected to a. predeterminedextension to function as a half-wave retardation device, means formounting one end of said sheet within said frame, and releasable meansmounted in said frame for subjecting said material to said predeterminedextension to vary the amount of light transmitted by said window.

4. In combination, frame means providing a window aperture, a pluralityof sheet-like, lightpolarizing elements at least of substantially thesame area as said aperture, means for mounting said elements insubstantially parallel relation within said frame With theirtransmission axes in predetermined relative angular relation, saidmounting means permitting linear movement of one of said elements, meansfor moving said movably mounted element with respect to the otherwithout changing the relative angular relation of the transmission axesthereof, and means comprising a sheet of light-transmitting, resilientmaterial capable of showing photoelastic eiects under stress positionedbetween said elements, said sheet; being secured at one end within saidframe, the opposite end being secured to said movable element.

5. A variable density window comprising, in combination, frame meansproviding a window aperture of substantial area, means providing alight-polarizing surface at least of substantially the same area as saidaperture and positioned within said frame means, means providing asecond light-polarizing surface positioned substantially parallel withand overlying said first-mentioned surface, light-transmitting materialpositioned between said polarizing surfaces and adapted, when subjectedto a predetermined strain, to function as a half-wave plate, saidmaterial being secured at one end to one of said light-polarizingsurfaces and at the opposite end to the other of said light-polarizingsurfaces, and means for moving at least one of said lightpolarizingsurfaces with respect to the other of said light-polarizing surfaces forsubjecting said f material to said predetermined strain.

EDWIN H. LAND.

